Film-forming resins have been used in hair care products (hair sprays, set lotions, etc.) to provide them with a good styling power or a lasting set-retaining power. Examples of these film-forming resins include polyvinyl pyrrolidone, polyvinyl pyrrolidone/vinyl acetate copolymers and vinyl acetate/crotonic acid copolymers.
It is required that a film-forming resin used in a hair care product enables the retention of a hair style for a long time and can be easily washed away with a shampoo or water.
Among the known polymers, however, those which are soluble in water suffer from a problem of becoming tacky under a high humidity due to their high hygroscopicity. That is to say, none of them satisfies both of the requirements of being tack-free even under a high humidity and exhibiting a good shampoo-washability. To overcome these problems, attempts have been made to reduce the tackiness while giving up the achievement of good shampoo-washability or to make the tackiness less conspicuous by using oily components such as silicone oil together with the polymers.
Moreover, a film made of such a water-soluble film-forming resin is softened due to water absorption, which makes it difficult to sufficiently sustain the hair style under a high humidity. When such a film-forming resin is used as a styling resin in an aerosol spray, furthermore, there arises another problem. That is to say, the film-forming resin is less soluble in hydrocarbons (LPG) commonly employed as propellant and, therefore, the aerosol composition should contain a further solvent (ethanol, isopropyl alcohol, etc.) in an elevated amount. As a result, the mist particles thus sprayed become large and heavy, which makes good styling difficult. In this case, furthermore, the resin film on the surface of the hair tends to peel off (so-called flaking) due to, for example, brushing. In this case, the gloss of the hair is deteriorated.
The present inventors have previously found a film-forming resin capable of sustaining a good set-retaining power even under a high humidity and applied it for a patent (EP-A-372546 and U.S. Pat. No. 5,278,269 corresponding to JP-A-2-180911; the term "JP-A" as used herein means an "unexamined published Japanese patent application"). However, this film-forming resin also suffers from a problem that it becomes tacky under a high humidity due to water absorption. Thus it has been still necessary to blend a specific oily component therewith so as to improve the texture.
Accordingly, an object of the present invention is to provide a film-forming resin which remains tack-free even under a high humidity, is capable of sustaining the hair style for a prolonged period of time, can be easily washed away with a shampoo or water, gives a good finishing when employed in an aerosol spray composition as a film-forming resin and causes no peeling of the film from the surface of the hair due to brushing.
Under these circumstances, the present inventors have further conducted extensive studies. As a result, they have successfully found out that it becomes possible to solve the problems mentioned above, while maintaining the fundamental performance of the film-forming resin of JP-A-2-180911, by employing a low-molecular weight (meth)acrylamide monomer as a substitute for the (meth)acrylate monomer constituting the copolymer of JP-A-2-180911, thus completing the present invention.